Cyanobacteria blooms: from impacts on the environment to management strategies

Master of ScienceDepartment of Biological & Agricultural EngineeringPhilip L. BarnesBloom-forming cyanobacteria are harmful to both environment and public health because of the release of water soluble toxins. This report provides a broad overview of cyanobacteria and cyanotoxins and the current state of knowledge about the bloom control management. Cyanobacteria blooms usually flourish in warm, lentic, and eutrophic waters. Several environmental factors such as temperature, nutrients, light intensity, and turbulence can affect cyanobacterial growth and the formation of bloom. Cyanobacteria can synthesize multiple types of toxins, which cause human and animal toxications worldwide. Cyanobacterial blooms also cause detrimental effects on aquatic ecosystems, and the taste and odor problems in drinking water supplies. Due to the adverse effects, treatments that are used for removing both cyanobacterial cells and aqueous cyanotoxins should be carried out once cyanobacterial blooms occur in freshwaters. Strategies based on physical, chemical, and biological methods are carried out to remove the cyanobacteria and cyanotoxins. All of these strategies have both advantages and disadvantages: some physical treatment methods can remove cyanotoxins within the intact molecules, but the cost is usually high and further processing is needed; some chemical methods are cheap and can degrade the cyanotoxins, however, the toxicological characterization of the chemical and the by-products needs to be investigated; some biological treatments are more environmentally friendly, but the long reaction time and some other external factors also pose some problems that affect the efficiency of the treatments. The paper concludes that the key to success is to find a reasonable balance between those advantages and disadvantages, and the specific conditions of each unique aquatic ecosystem should be taken into consideration. As well, some suggestions are also proposed for the further development of more robust monitoring and management strategies

The effect of sample size re-estimation on type I error rates when comparing two binomial proportions

Master of ScienceDepartment of StatisticsChristopher I. VahlEstimation of sample size is an important and critical procedure in the design of clinical trials. A trial with inadequate sample size may not produce a statistically significant result. On the other hand, having an unnecessarily large sample size will definitely increase the expenditure of resources and may cause a potential ethical problem due to the exposure of unnecessary number of human subjects to an inferior treatment. A poor estimate of the necessary sample size is often due to the limited information at the planning stage. Hence, the adjustment of the sample size mid-trial has become a popular strategy recently. In this work, we introduce two methods for sample size re-estimation for trials with a binary endpoint utilizing the interim information collected from the trial: a blinded method and a partially unblinded method. The blinded method recalculates the sample size based on the first stage’s overall event proportion, while the partially unblinded method performs the calculation based only on the control event proportion from the first stage. We performed simulation studies with different combinations of expected proportions based on fixed ratios of response rates. In this study, equal sample size per group was considered. The study shows that for both methods, the type I error rates were preserved satisfactorily

Calibration of the Radical Installation Limit Error of the Accelerometer in the Gravity Gradient Instrument

Gravity gradient instrument (GGI) is the core of the gravity gradiometer, so the structural error of the sensor has a great impact on the measurement results. In order not to affect the aimed measurement accuracy, limit error is required in the installation of the accelerometer. In this paper, based on the established measuring principle model, the radial installation limit error is calibrated, which is taken as an example to provide a method to calculate the other limit error of the installation under the premise of ensuring the accuracy of the measurement result. This method provides the idea for deriving the limit error of the geometry structure of the sensor, laying the foundation for the mechanical precision design and physical design

Mathematical Modeling of the Working Principle of Gravity Gradient Instrument

Gravity field is of great significance in geoscience, national economy and national security, and gravitational gradient measurement has been extensively studied due to its higher accuracy than gravity measurement. Gravity gradient sensor, being one of core devices of the gravity gradient instrument, plays a key role in measuring accuracy. Therefore, this paper starts from analyzing the working principle of the gravity gradient sensor by Newton's law, and then considers the relative motion between inertial and non-inertial systems to build a relatively adequate mathematical model, laying a foundation for the measurement error calibration, measurement accuracy improvement

Genomic assessment of quarantine measures to prevent SARS-CoV-2 importation and transmission

Mitigation of SARS-CoV-2 transmission from international travel is a priority. We evaluated the effectiveness of travellers being required to quarantine for 14-days on return to England in Summer 2020. We identified 4,207 travel-related SARS-CoV-2 cases and their contacts, and identified 827 associated SARS-CoV-2 genomes. Overall, quarantine was associated with a lower rate of contacts, and the impact of quarantine was greatest in the 16–20 age-group. 186 SARS-CoV-2 genomes were sufficiently unique to identify travel-related clusters. Fewer genomically-linked cases were observed for index cases who returned from countries with quarantine requirement compared to countries with no quarantine requirement. This difference was explained by fewer importation events per identified genome for these cases, as opposed to fewer onward contacts per case. Overall, our study demonstrates that a 14-day quarantine period reduces, but does not completely eliminate, the onward transmission of imported cases, mainly by dissuading travel to countries with a quarantine requirement

Optimized Design of the SGA-WZ Strapdown Airborne Gravimeter Temperature Control System

The temperature control system is one of the most important subsystems of the strapdown airborne gravimeter. Because the quartz flexible accelerometer based on springy support technology is the core sensor in the strapdown airborne gravimeter and the magnet steel in the electromagnetic force equilibrium circuits of the quartz flexible accelerometer is greatly affected by temperature, in order to guarantee the temperature control precision and minimize the effect of temperature on the gravimeter, the SGA-WZ temperature control system adopts a three-level control method. Based on the design experience of the SGA-WZ-01, the SGA-WZ-02 temperature control system came out with a further optimized design. In 1st level temperature control, thermoelectric cooler is used to conquer temperature change caused by hot weather. The experiments show that the optimized stability of 1st level temperature control is about 0.1 °C and the max cool down capability is about 10 °C. The temperature field is analyzed in the 2nd and 3rd level temperature control using the finite element analysis software ANSYS. The 2nd and 3rd level temperature control optimization scheme is based on the foundation of heat analysis. The experimental results show that static accuracy of SGA-WZ-02 reaches 0.21 mGal/24 h, with internal accuracy being 0.743 mGal/4.8 km and external accuracy being 0.37 mGal/4.8 km compared with the result of the GT-2A, whose internal precision is superior to 1 mGal/4.8 km and all of them are better than those in SGA-WZ-01

Global Patch Matching (GPM) for freehand 3D ultrasound reconstruction

Abstract Background 3D ultrasound volume reconstruction from B-model ultrasound slices can provide more clearly and intuitive structure of tissue and lesion for the clinician. Methods This paper proposes a novel Global Path Matching method for the 3D reconstruction of freehand ultrasound images. The proposed method composes of two main steps: bin-filling scheme and hole-filling strategy. For the bin-filling scheme, this study introduces two operators, including the median absolute deviation and the inter-quartile range absolute deviation, to calculate the invariant features of each voxel in the 3D ultrasound volume. And the best contribution range for each voxel is obtained by calculating the Euclidian distance between current voxel and the voxel with the minimum invariant features. Hence, the intensity of the filling vacant voxel can be obtained by weighted combination of the intensity distribution of pixels in the best contribution range. For the hole-filling strategy, three conditions, including the confidence term, the data term and the gradient term, are designed to calculate the weighting coefficient of the matching patch of the vacant voxel. While the matching patch is obtained by finding patches with the best similarity measure that defined by the three conditions in the whole 3D volume data. Results Compared with VNN, PNN, DW, FMM, BI and KR methods, the proposed Global Path Matching method can restore the 3D ultrasound volume with minimum difference. Conclusions Experimental results on phantom and clinical data sets demonstrate the effectiveness and robustness of the proposed method for the reconstruction of ultrasound volume

Denoising results with three parameters and two stages.

<p>(a) LDCT image; (b) SDCT image; (c), (f), and (i) are the LDCT images denoised with <i>P</i> = 2, <i>P</i> = 3, and <i>P</i> = 4 in the first stage, respectively; (d), (g), and (j) are the LDCT images denoised with <i>P</i> = 2, <i>P</i> = 3, and <i>P</i> = 4 in the second stage, respectively; (e), (h), and (k) are the zoomed regions specified in (a).</p

Standard deviations of different ROIs for the original image, noisy image, and denoised images in the four stages.

<p>Standard deviations of different ROIs for the original image, noisy image, and denoised images in the four stages.</p

STDs of seven ROIs for LDCT, SDCT, and processed LDCT images of a 61-year-old female patient with liver tumor.

<p>STDs of seven ROIs for LDCT, SDCT, and processed LDCT images of a 61-year-old female patient with liver tumor.</p